Each bag contains a polymer which expands when it comes into contact with water, absorbing up to 100 times its own weight. When placed in a toilet cistern, the bag expands to displace 1.2 litres of water every flush, saving a family of four about 10,000 litres a year, and about £30 on their annual water bill.

Southern Water is giving the Save-a-Flush bags away free to its customers to promote water efficiency in support of its water meter installation programme, which is currently being rolled out across the South East.

The bags will be manufactured by Sussex-based firm A E Adams, which has been awarded the contract by Dry Planet. The firm, which has been manufacturing the product for a number of years, is now set to expand its production capacity to cope with growing demand.

"We are always looking for opportunities to award contracts to companies local to our region and we are delighted with our new range of Save-a-Flush bags," said Southern Water metering programme commercial manager Malcolm Butchers. "It's great to see manufacturing thriving in the South East and by producing these locally, we also cut down on travel costs, reducing our carbon footprint."